1. Field of the Invention
The invention relates to chemical mechanical polishing (CMP) polisher and more particularly to an in-situ slurry mixing apparatus for the CMP polisher.
2. Description of the Related Art
Due to the increasingly high integration of ICs, chips simply cannot provide sufficient area for manufacturing interconnections. Therefore, in accord with the increased interconnects manufacturing requirements of miniaturized MOS transistors, it is increasingly necessary for IC manufacturing to adopt a design with more than two metal layers. Planarization is an important technology in semiconductor process. The surface of the wafer has an even topography after planarization and it is able to prevent exposure light source from being scattered, so that the pattern transfer can be carried out precisely. Additionally, planarization is also a main factor that affects the accuracy of the alignment system. If the flatness of the wafer is poor, the mask cannot be aligned the wafer by the alignment system and the probability of making mistakes in the process is increased.
CMP is currently the only process that can provide global planarization in very large scale integration (VLSI) and ultra-large scale integration (ULSI). CMP is a planarization process that planarizes an uneven surface by applying mechanical polishing and adding a suitable chemical reagent called slurry. Generally. slurry is formed by a composition of the abrasive particles such as colloidal silica or dispersed alumina and a basic solution such as potassium hydroxide solution or ammonium.
The quality of the slurry determines the stability of the process, so it is important in the planarized process of CMP. Chemical reaction and mechanical polishing are determined by chemical reagent and particles in the slurry, respectively. The slurry first needs to be diluted by solvent, after which it is ready for use, so that the slurry is varied depending of the material to be polished, and it is often necessary to use two kinds of slurry to planarize a wafer.
Since the slurry needs to be diluted to a suitable concentration, a premixer is added in the slurry supplier to mix slurry in advance. However, the property of the slurry may easily change after mixing. Thus, the slurry has to be consumed after being mixed and before reaching a Pot life. Due to the instability of the pre-mixed slurry, another in-situ slurry mixing apparatus is developed. However, the mixing time of the in-situ slurry mixing apparatus is too short to uniformly mix the slurry, so that the quality of the slurry cannot be easily controlled. Moreover, the nonuniform mixing slurry would result in a worse CMP performance, so that the flatness of the wafer is poor and misalignment occurs easily.